Normalization With No Duplicates

I have a PO DB that I'm trying to normalize. For the most part it is normalized but there are 2 fields that are not normalized because they repeat data. So I'm trying to restructure a bit and having some problems when it comes to data entry via forms.

There is also a PO table above this one but is not used in the subform for the details.
My old set up for my PODetailsTable

PODetailsID pk
PO fk
Item
Quantity
Price
Allocation

I want my new set up to be
PODetailsTable

PODetailsID pk
PO
ItemID fk
Quantity
Price
AllocationID fk

ItemTable
ItemID pk
Item

AllocationTable
AllocationID pk
Allocation

On my form I can't enter anything that is already on the ItemTable. I looked at some microsoft sample DB's and they have you enter the item from a different form then you can select it in from the combo box which would really slow down data entry peticularly early on.

Is there a way I can type the Item in and if its new, it will be put it on the ItemTable associate an ItemID to both tables?? But if its already in the Itemtable just apply the already existing PK on ItemTable to the FK ItemID on the PODetails Table for that record??

Here is a A2K format of it which is how it currently works. In the relationships window you can see an example of how I want it but can't get to work.

17501

Thanks JOe K.